<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="../vue.2.5.1.js"></script>
</head>

<body>
    <div id="sky">
        <div>
            {{res}}
        </div>
        <div>
            {{firstName}}
        </div>
        <div>
            {{lastName}}
        </div>
    </div>
    <script>
        var app = new Vue({
            el: "#sky",
            data: {
                firstName: "sky",
                lastName: "moon"
            },
            computed: {
                res: {
                    get: function() {
                        return this.firstName + "a n d" + this.lastName;
                    },
                    set: function(val) {
                        var val_ = val.split(" ");
                        this.firstName = val_[0];
                        this.lastName = val_[val_.length - 1]

                    }
                }
            }
        })
    </script>
</body>

</html>